I don't understand. So now the URL bar won't always show where the page was actually loaded from? It could show example.com but really be loaded from Google'S AMP servers? If I'm reading this right, I find it very sad.
Web Packaging [https://github.com/WICG/webpackage] allows the authority over an origin to delegate serving to a third party (and support things like offline serving). This is similar, but better than e.g. what a CDN does today, because the third party does not need access to the private key.